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#1276 2021-06-29 20:22:54

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 23,084

Re: Starship is Go...

Nasa selected one company but broke its rules by claiming it needed money to be able to have others.
Change the price tag on the contracts sounds about right. Also when you ask for something specific and another delivers something that is not it for the contract thats a violation and should not be given favor....

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#1277 2021-06-30 14:52:28

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,863

Re: Starship is Go...

BN3 is fully stacked in the High Bay!

https://www.reddit.com/r/spacex/comment … ed_in_the/


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#1278 2021-07-02 06:18:11

NewMarsMember
Member
Registered: 2019-02-17
Posts: 232

Re: Starship is Go...

Message from GW Johnson via Portal ...

Gary Johnson
Jul 1, 2021, 5:08 PM (15 hours ago)

I did as I said I might.  I wrote another ramjet article about my work on ASALM-PTV decades ago.  I just posted the thing on "exrocketman".  It picks up where the SA-6 exploitation article left off.

I see in post 1275 of "Starship is Go" under "Human Missions" that Louis is still insisting that a Mars Starship will land on exposed level bedrock.  Not with a narrow stance of legs that lack hydraulic shock absorption it won't! 

Besides,  99% of Mars is soft dry sands with rocks dispersed in it,  without any cohesion between sand grains (!!!),  and without any cohesion between the sand and the embedded rocks(!!!).  That is the very definition of regolith,  by the way.  The other 1% of Mars is hard rock,  but very, very little of it is smooth,  much less level. 

I would bet on the soft sand in order not to restrict my choices of landing sites,  and just use large footpads on the landing legs to handle the soft sand.  And I would use wide-stance legs with hydraulic shock absorption to handle (with impunity) rough,  uneven,  or sloping ground,  plus boulders-as-obstructions,  and any potholes or creek beds.  I've already figured out how much pad area is needed.  And refilling for takeoff is the weight that sizes pads,  not touchdown weight,  even factored up for dynamic impact effects.  And yes,  I figured weights from masses at 38% gee.

99% sand versus way-under-1% hard,  smooth,  level rock.  Louis is backing a very BAD bet!  We old-hand engineers know better than that.  Murphy's Law is not a joke,  it is a way to survive when venturing into the unknown.  And don't let anybody kid you about how good the remote sensing is.  It is still crap,  although it is much better than it was in the 1970's.

GW


Thomas Hanson
8:15 AM (0 minutes ago)
to Gary

For Dr. Johnson,
Thanks for news of your new blog article!  I'll post your message shortly.
Best wishes to Mrs. Johnson for her health challenges!
Glad to see her laptop is still reliable for the blog and email.

(th)

Last edited by NewMarsMember (2021-07-02 06:19:15)


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#1279 2021-07-02 14:26:25

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,863

Re: Starship is Go...

Thanks for relaying Gary's thoughts, New Mars Member...

The Erebus Montes area appears to be the current JPL/Space X favourites region for potential landing sites.

https://en.wikipedia.org/wiki/Erebus_Montes

https://www.geekwire.com/2019/nasa-chec … ater-mind/

Reading up the Mars human landing site workshops conference from a couple of years ago (still the best resources I think):

https://www.nasa.gov/feature/mars-human … entations/

we can see that the main requirements are

- shallow gradient angle  (less than 5 degrees preferably but 10 degrees probably the max)

- absence of large individual rocks that could compromise a landing

- low levels of dust

Mountains are made of rock by definition, but of course the slopes will generally tend to be too extreme for a landing site. However there may be some lower slopes of mountains which will be acceptable.

So taking all these factors into account it seems to me that a rocky "platform" would be ideal.

They do exist on Earth - often found in coastal areas as wave cut platforms. I think the Erebus Mountains would have been islands in the Northen Ocean, so there might well be wave cut platforms around them.

Happy to accept I may be wrong, but if such platforms did exist with a low gradient they could be the ideal landing areas.

I have no doubt Starships could land on rock fields but the fear of engine damage is a real one.  It may be possible to take replacement engines to Mars in one of the Starships but how to fit them would be problematical I imagine.

As for landing on sand, well sand is another way of saying dust (cf dust storms). And dust damage is certainly a concern to the people looking at human landing sites (as set out in the above NASA workshop link).

The only other alternative I can think of is clay. But what happens to clay when blasted with rocket exhaust? Hmmmm...

One other thought - could you come in for a landing semi-horizontal and then suddenly go vertical in the last few seconds. Would that redcue the risk of damage to the engines?

NewMarsMember wrote:

Message from GW Johnson via Portal ...

Gary Johnson
Jul 1, 2021, 5:08 PM (15 hours ago)

I did as I said I might.  I wrote another ramjet article about my work on ASALM-PTV decades ago.  I just posted the thing on "exrocketman".  It picks up where the SA-6 exploitation article left off.

I see in post 1275 of "Starship is Go" under "Human Missions" that Louis is still insisting that a Mars Starship will land on exposed level bedrock.  Not with a narrow stance of legs that lack hydraulic shock absorption it won't! 

Besides,  99% of Mars is soft dry sands with rocks dispersed in it,  without any cohesion between sand grains (!!!),  and without any cohesion between the sand and the embedded rocks(!!!).  That is the very definition of regolith,  by the way.  The other 1% of Mars is hard rock,  but very, very little of it is smooth,  much less level. 

I would bet on the soft sand in order not to restrict my choices of landing sites,  and just use large footpads on the landing legs to handle the soft sand.  And I would use wide-stance legs with hydraulic shock absorption to handle (with impunity) rough,  uneven,  or sloping ground,  plus boulders-as-obstructions,  and any potholes or creek beds.  I've already figured out how much pad area is needed.  And refilling for takeoff is the weight that sizes pads,  not touchdown weight,  even factored up for dynamic impact effects.  And yes,  I figured weights from masses at 38% gee.

99% sand versus way-under-1% hard,  smooth,  level rock.  Louis is backing a very BAD bet!  We old-hand engineers know better than that.  Murphy's Law is not a joke,  it is a way to survive when venturing into the unknown.  And don't let anybody kid you about how good the remote sensing is.  It is still crap,  although it is much better than it was in the 1970's.

GW


Thomas Hanson
8:15 AM (0 minutes ago)
to Gary

For Dr. Johnson,
Thanks for news of your new blog article!  I'll post your message shortly.
Best wishes to Mrs. Johnson for her health challenges!
Glad to see her laptop is still reliable for the blog and email.

(th)


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#1280 2021-07-02 16:56:04

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,221

Re: Starship is Go...

The issue of massive dust cloud displacement from the Mars landing hasn't really been addressed on this forum. Maybe this is why Musk has jumped into the lunar landing program, because it will address a similar if not more extreme issue on the moon. Landing legs and lotsa fire from the engines exhaust aren't a particularly compatible situation.

My thoughts:

Use the similar engine arrangement for both lunar lander and Mars landing Starships, with engines high on the body of the landing vehicle with exhausts angled away from the touchdown point. Landing legs could be a part of a dockable extension attached in LEO after refueling the Starship for the Hohman transfer maneuver. After Mars departure on the return flight back to Earth, those wide tracked legs could simply be left behind and landing on a prepared pad accomplished at Starbase.

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#1281 2021-07-02 18:12:25

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,863

Re: Starship is Go...

Well, I think this is why I come back to the rock platform.

Every other sort of surface risks engine damage - which could seriously compromise the return element of the Mission and/or risk an explosion on landing.

I think we need first to establish if such rock platforms exist.


Oldfart1939 wrote:

The issue of massive dust cloud displacement from the Mars landing hasn't really been addressed on this forum. Maybe this is why Musk has jumped into the lunar landing program, because it will address a similar if not more extreme issue on the moon. Landing legs and lotsa fire from the engines exhaust aren't a particularly compatible situation.

My thoughts:

Use the similar engine arrangement for both lunar lander and Mars landing Starships, with engines high on the body of the landing vehicle with exhausts angled away from the touchdown point. Landing legs could be a part of a dockable extension attached in LEO after refueling the Starship for the Hohman transfer maneuver. After Mars departure on the return flight back to Earth, those wide tracked legs could simply be left behind and landing on a prepared pad accomplished at Starbase.

Last edited by louis (2021-07-02 18:23:07)


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#1282 2021-07-02 18:18:53

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 23,084

Re: Starship is Go...

So a version of the super draco engines with in the shell walls with a channel heatshield to funnel the exhaust at the slant as seen in the crewed dragon. All to avoid a concentrate cone blasting of the regolith of the moon or mars.

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#1283 2021-07-02 22:57:25

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,221

Re: Starship is Go...

Mostly to avoid damage to the engines from flying debris, or in the case of the moon--sending stones and debris into low lunar orbit. The early designs of Robert Goddard as well as those of the German program of Herman Oberth & von Braun all used tractor style designs instead of more commonly seen today--"pusher" style designs.

Flame diverters are avoided in both takeoff and landings.

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#1284 2021-07-03 07:00:49

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,863

Re: Starship is Go...

So more like an abort rocket?

https://upload.wikimedia.org/wikipedia/ … test_1.jpg

This would certainly require a major design which nothing from Musk has suggested is in the offing.



Oldfart1939 wrote:

Mostly to avoid damage to the engines from flying debris, or in the case of the moon--sending stones and debris into low lunar orbit. The early designs of Robert Goddard as well as those of the German program of Herman Oberth & von Braun all used tractor style designs instead of more commonly seen today--"pusher" style designs.

Flame diverters are avoided in both takeoff and landings.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#1285 2021-07-03 07:03:25

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,863

Re: Starship is Go...

BN3 being rolled out for ground testing.

BN4 scheduled as first orbital rocket.

Do people think getting the Boosters right is more or less difficult than getting the Starships right? I'm assuming more on the basis there are more engines...or is there some inbuilt redundancy?


https://www.space.com/spacex-starship-s … bbf865be49


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#1286 2021-07-03 09:59:44

NewMarsMember
Member
Registered: 2019-02-17
Posts: 232

Re: Starship is Go...

Here is another update from GW Johnson ...

Gary Johnson
11:13 AM (43 minutes ago)

This is for the forums,  specifically "human missions" / "starship is go".

1. I see discussions whether to use pusher or tractor rockets to land on Mars in posts 1280 through 1284.  Tractor reduces thrown debris,  true enough.  But the danger is not to the engines of the ship that lands,  it is to adjacent structures,  and therefore is no risk to anyone for the first ship down.  The Apollo LEM proved there is no danger to the engine or engines of the ship that lands,  as did Surveyor 3 before it.  Both used pusher engines. Same is true for Viking (and nearly everything since) on Mars.

Once there are multiple ships trying to land at the same site,  that is where the danger to adjacent structures is high.  Rocks thrown by the exhaust may well be flying away at hundreds or even thousands of m/s.  In the lower gravity,  they may well fly many km.  That is where tractor rockets will help mitigate the risk: vastly lower tendency to throw rocks,  and at lower speeds.  THAT is what the old experts in the 1930's were trying to achieve with tractor rocket designs.

2. I also see discussions on the large number of engines in the Superheavy test articles,  in post 1285.  There are supposed to be something like 28 Raptors powering the Superheavy in the first flight or two.  Later on,  this is supposed to be 30-something,  and I'm not sure even Spacex knows yet how many.  But weight-at-takeoff vs factor 1.5 desired on the takeoff thrust-to-weight ratio,  suggests this will be near 36 engines.  Statistics say if each engine has a super-high reliability,  the more engines is more reliability overall.  If the individual engine reliability is not super-high,  then the probability of failure actually increases with more engines,  instead of decreasing.  Sometimes redundancy shoots you in the foot,  instead of doing what you intended.

Spacex has already demonstrated 27 Merlins would work with Falcon Heavy.  That's a positive.  Their Raptors do not yet have that track record,  but soon they must,  or this project will fail.  A negative would be the Russian experience with the N-1 moon rocket in the late 1960's,  crudely comparable to Superheavy,  being larger than Saturn-5.  It had 30-something engines in its first stage,  and never once flew successfully.  The failure mode they could not fix was one engine having an "unscheduled rapid disassembly",  triggering the ones next to it to also explode.  This cascaded around the booster,  until the whole rocket exploded. Sort of a chain reaction.

The fix is either make the engines so reliable they will never explode,  or else carry the weight of the armor that stops the chain reaction of exploding engines triggering more exploding engines.  Neither option is easy.

GW

(th)


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#1287 2021-07-03 10:54:11

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,573
Website

Re: Starship is Go...

Just testing after my wife ran some anti-malware stuff on her machine.

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#1288 2021-07-03 11:59:23

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 23,084

Re: Starship is Go...

Holy Batman, plausible success in the wind.

Nice post to comparison of engine count of a Falcon 9 heavy which makes one wonder if 3 core would not be better than a single large booster.

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#1289 2021-07-03 13:21:07

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,573
Website

Re: Starship is Go...

I'm astonished myself,  Spacenut.  Glad to be back!

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#1290 2021-07-03 15:35:59

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,221

Re: Starship is Go...

Welcome back!

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#1291 2021-07-03 16:08:55

kbd512
Administrator
Registered: 2015-01-02
Posts: 4,614

Re: Starship is Go...

Welcome back, GW.

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#1292 2021-07-03 16:36:23

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 6,742
Website

Re: Starship is Go...

Gary is back! Yea! Welcome back!
de80b8eff4b321ad35c213de9b82ab76.gif

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#1293 2021-07-06 13:16:13

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,863

Re: Starship is Go...

Welcome back Gary, you might enjoy these graphics if you haven't seen them yet...

https://www.youtube.com/watch?v=AE1TcxSB9iA


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#1294 2021-07-06 13:21:43

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,863

Re: Starship is Go...

Latest video from SpaceXCentric - good update.

https://www.youtube.com/watch?v=DuXgueL-y50


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#1295 2021-07-08 21:14:33

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,221

Re: Starship is Go...

I was watching a couple YouTube programs, and it seems that Elon is now considering a tether system between 2 Starships for production of artificial gravity. No doubt the influence of Robert Zubrin?

https://www.youtube.com/watch?v=fTCpHiy60RA

Last edited by Oldfart1939 (2021-07-08 21:17:33)

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#1296 2021-07-09 04:54:22

louis
Member
From: UK
Registered: 2008-03-24
Posts: 6,863

Re: Starship is Go...

Interesting, I get the impression that a tether system won't be for Mission One. It could revolutionise space tourism. It could also be the basis for successful reproduction on Mars if you had a 1G facility in LMO where women could go to be pregnant - allowing for safe foetal development.

Oldfart1939 wrote:

I was watching a couple YouTube programs, and it seems that Elon is now considering a tether system between 2 Starships for production of artificial gravity. No doubt the influence of Robert Zubrin?

https://www.youtube.com/watch?v=fTCpHiy60RA


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#1297 2021-07-09 18:17:10

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 23,084

Re: Starship is Go...

Well for fuel delivery the ship will need to be able to produce AG so its once we get one to orbit to bring down to earth that we will be ready for that next coupling step.

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#1298 2021-07-10 10:06:12

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,573
Website

Re: Starship is Go...

What you are seeing here is the effect of even Spacex not yet knowing what the final designs for its "Starship" vehicles are going to be.  Not for refilling "gravity",  not for landing legs,  not even for the tanker version. 

Yeah,  you could tether two vehicles and rotate slowly on a long tether to produce whatever gee you want up to around 1 gee.  If you tied the tether somehow to their noses (there are currently no published Spacex design concepts for that),  you get that gee such that "down" is the same direction as when the vehicle is sitting on its tail on the ground somewhere. 

Your effective gravity is = (your radius/56 m radius)*(your rotation rate/4 rpm)^2,  where there is an effective long-term (!!!) adaptation limit of 4 rpm or less. 

Spacex has published concepts for refill by docking two Starships tail-to-tail.  The published refill concept has thruster firing in one ship to provide micro-acceleration to the docked cluster,  such that the resulting micro-gravity (no gee level specified by Spacex) allows propellants to run "downhill" to the other ship. 

That same docked geometry would be around 90 m long from manned space to manned space.  That's a spin radius of 45 m.  If you were to spin that cluster end-over-end at 4 rpm, your effective gravity would be pretty near 45/56~ 0.8 gee.  Slower spin is lower gee.  The only real trouble with this concept is that "down" is toward the nose of the ship,  not the tail as when sitting on the ground somewhere.  It's an appurtenance design problem,  not anything fundamental.  The advantage is you are spinning a rigid body like a baton,  something we know is stable,  without running any cable-oscillation risks at all.

No one has ever demonstrated stable cable-tethered spin gravity at anything above .001 to .01 gee.  That was done in the 1960's with a Gemini-Agena rig. 

I see lots of proposals to use cable-tethers for spin gravity,  but I have NEVER,  EVER seen any experimental results to back them up,  at useful gee levels (which would be 0.1 to 1 gee).  Such are therefore BY DEFINITION not an off-the-shelf,  ready-to-apply technology for design purposes.  Not until the necessary experiments at useful gee levels have been successfully run.  And the odds favor failure first time up.

GW

Last edited by GW Johnson (2021-07-10 10:10:17)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#1299 2021-07-10 10:27:37

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,221

Re: Starship is Go...

I doubt that the tether system would be used to generate 1 g. I would anticipate that on the outbound to Mars flight, it would be 0.4 g, which would reduce the necessary weight of the tether cable substantially, as less tensile forces would be involved. It would also reduce the spin rate to employ such a system. Arriving Mars colonists would be adapted to living and working in a lower gravitational environment. Such a system would be advantageous for food preparation, bathing, and using a toilet.

Of course, all the freight carriers would be absent this system. Not needed.

I really think that Elon may have thought "too big," for the passenger Starships. Smaller crewed ships would have been better for the first several years of missions to the Red Planet. The monsters he's creating will be the supply system for the first few decades of colonization. But--it's his money and his company. If he succeeds, he will become a civilization savior.

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#1300 2021-07-10 11:28:08

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 7,313

Re: Starship is Go...

For GW Johnson re #1298

Please evaluate a rigid truss mounted between the noses of two starships.

Such a truss could be lifted to orbit in a Starship and then fitted to one of two starships before acceleration to Mars.

After both vessels are safely on their way, they can be maneuvered into position for docking with the truss, spun up and maintained in that configuration on the way to Mars.  Upon arrival, the two would be despun, one would undock, and if both vessels are intended to land, the truss could be left in orbit for the return trip.

Please estimate (to the extent possible) the options Elon and company might have for a system of this kind.

***
PS ... the North Houston Chapter of the National Space Society is holding it's last full Virtual meeting today at 2 PM Houston time.

If your wife's laptop supports Zoom, you would be welcome to log in.

You don't have to provide video if you don't want to.

I think that you'll be favorably impressed by the credentials of some of the attendees.

(th)

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